Back during the late Miocene period, about 9 million years ago, two large and ferocious predators shared the same ecological niche. The two species, the leopard-sized sabre-toothed cat (Promegantereon ogygia) and the much larger, lion-sized bear dog (Machairodus aphanistus), somehow managed to avoid each other and share the resources of the same woodland habitat. Looking to find out how they achieved this apparent harmony, a team of paleontologists took a closer look at their fossilized remains.

To do so, a collaborative research team from the University of Michigan and the Museo Nacional de Ciencias Naturales in Madrid conducted a series of tests in which stable carbon isotypes of the animals' teeth were analyzed, providing them with a glimpse into their eating habits. The researchers, a team led by Soledad Domingo, used a standard dentist's drill to extract samples from nearly 70 specimens that lived at the time, including 42 herbivores and 27 saber-toothed cats and bear dogs. The remains were found in geological pits near Madrid, Spain.

Once the researchers isolated the carbon from the tooth enamel, they used a mass spectrometer to measure the various organic elements present in the teeth (different animals will leave different isotropic signatures depending on what they eat). Once the various compounds were mapped according to species, the researchers could start to determine who was eating what.

What they discovered was that the saber-tooth cats and bear dogs did in fact hunt the same prey — but that the prey were occupying slightly different portions of habitat (they were able to determine this by looking at the different kinds of plants that the herbivores were eating).

Based on this, the researchers determined that the big cats could avoid the larger bear dogs by using the ample tree cover to conceal themselves while hunting for such things as horses and wild boar. The bear dog, on the other hand, in addition to preying on the same animals, also likely hunted antelope in more open areas that overlapped with the cats' territory, just slightly separated. This way, the two animals could avoid unpleasant encounters with each other — even if there was some overlap in their prey.

Consequently, these two sympatric predator animals could inhabit the same geographic area and partition resources accordingly.